Sound localization and its neural correlates will be studied with neurophysiological, anatomical and behavioral techniques in owls and cats. The auditory system of the owl is highly adapted for deriving the location of sound in space. Space-specific neurons are excited by sound only when the source is located within a restricted receptive field; in the owl's optic tectum and inferior colliculus, these neurons are organized systematically according to the locations of their fields thereby forming maps of auditory space. We will determine the physical basis of auditory receptive fields by characterizing the effects of stimulus intensity, frequency, and interaural differences in time and intensity on the responses of space-specific neurons in the optic tectum. In addition, we will seek those differences in the stimulus selectivities of neurons that give rise to the maps of space. The sensitivity of neurons in the optic tectum of the cat to sound location will be characterized to provide insights into general principles of space coding in the auditory system. Sound localization is shaped by early auditory experience in owls. We will determine the critical period, extent, and time course of this process, and its dependence on visual feedback. Physiological and anatomical correlates will be sought to elucidate the mechanisms by which the auditory system modifies its connectivity based on experience. Knowledge of the neural and anatomical mechanisms underlying sound localization and the susceptibility of these mechanisms to modification by experience will lead to effective treatment of the perceptual deficits caused by hearing loss or brain dysfunction, and will increase our understanding of the auditory system and the ways in which the brain processes sensory information to extract features of the environment that are not directly coded in the sensory input.